1. Field of the Invention
The present invention relates to a wireless communication device, a network, a wireless communication method, and a program that causes a computer to execute the method.
2. Description of Related Art
In recent years, wireless LAN (Local Area Network) communication has become common not only in companies' workplaces, but also in a variety of fields including homes and outdoors. Because the use of wireless LAN has become widespread, there has been an increase in the traffic in available frequency resources, that are limited, thereby creating serious concern about communication interference.
IEEE 802.11, which is one of the wireless LAN standards, uses an access control technique that is referred to as carrier sense multiple access with collision avoidance (CSMA/CA). This access control technique has a feature in which each wireless communication device starts communication after determining whether or not the neighboring wireless communication devices are generating radio waves.
In the foregoing access control technique, to avoid a communication collision, a wireless communication device of interest determines whether or not a neighboring device (another wireless communication device) is generating a radio wave. If the neighboring device is generating a radio wave, the device of interest waits for a predetermined time (back-off time) and then determines again whether or not the neighboring device is generating a radio wave. If the neighboring device is not transmitting a radio wave, the device of interest transmits a radio wave after the elapse of a random time. The wireless communication device of interest uses a carrier sense scheme so as to determine whether or not the neighboring device is generating a radio wave.
In the carrier sense scheme, the wireless communication device checks for the use of a radio channel. If the device detects the preamble of a signal that complies with the IEEE 802.11 standard (synchronization establishment signal), since the device receives the signal, the radio channel becomes busy. If the wireless communication device cannot receive the preamble of the signal that complies with the IEEE 802.11 standard and detects a power level that is greater than a predetermined carrier sense threshold, the wireless communication device determines that the radio channel is busy and waits to transmit a signal. In contrast, if the wireless communication device detects a power level lower than the predetermined carrier sense threshold, the wireless communication device determines that the radio channel is idle.
The foregoing access control technique has the following problem. In the following description, a wireless communication device that complies with IEEE 802.11 is referred to as “802.11 wireless device.”
The CSMA/CA scheme used to control transmission and reception for an 802.11 wireless device has a problem in which, due to an external interference, a packet collision cannot be fully avoided. In addition, since a packet collision cannot be detected, if a communication failure occurs due to a packet collision, the cause of the communication failure cannot be identified and thereby effective prevention measures cannot be implemented. If a packet collision occurs due to external interference, since there are no means to quantitatively calculate the collision rate, it is difficult to accurately evaluate the collision rate.
A packet collision detection technique disclosed in JP 09-64884A Publication (hereinafter referred to as Patent Literature 1) simultaneously transmits a signal and observes the signal over a transmission path, removes the transmission signal from the observed signal, and determines whether or not a signal collision occurs over the transmission path based on the energy amount of the signal from which the transmission signal was removed.
An alternative packet detection technique disclosed in JP 2010-23387A Publication (hereinafter referred to as Patent Literature 2) calculates data collision likelihood based on the number of neighboring wireless terminals, radio transmission rates, and so forth.
Although the technique disclosed in Patent Literature 1 can determine whether or not there is an interference signal other than a transmission signal, it cannot determine whether or not the measured interference signal interferes with a signal received on the reception side. In addition, although a signal that the transmission side cannot measure may interfere with a signal received on the reception side, the technique cannot detect the interference.
The technique disclosed in Patent Literature 2 calculates the data collision likelihood based on the predicted wireless communication state. If the predicted wireless communication state largely differs from the real wireless communication state, the calculated collision rate will not comply with the real wireless communication state. The techniques disclosed in Patent Literature 1 and Patent Literature 2 can not detect packet collisions with sufficient accuracy. Thus, countermeasures to improve data transmission efficiencies cannot be taken.
In addition, the influence of external interference of wireless LAN communication depends on the interference distance and the power intensity of the interference wave. Thus, an 802.11 wireless device cannot accurately identify such different interference states. As a result, countermeasures to improve data transmission efficiencies cannot be taken based on interference states.